1. Technical Field
The present invention relates to a coating device and a coating method. In particular, the present invention relates to a coating device and a coating method in which, even when coating a highly viscous coating liquid onto a strip-shaped body while conveying the strip-shaped body at high speed, local absence of the coating liquid due to the accompanying air which is brought in together with the strip-shaped body does not arise.
Moreover, the present invention relates to a coating device and a coating method in which, in a coating device which has a bar which coats a coating liquid on a strip-shaped body conveyed in a given direction and a dam-shaped member disposed at the upstream side of the bar, can effectively prevent problems at the coated surface which are caused by stuck matter which arises at the dam-shaped member at the upstream side.
2. Description of the Related Art
A planographic printing plate undergoes processes as follows to be fabricated. Commonly, at least one face of an aluminium web formed of pure aluminium or an aluminium alloy is dressed. Then an electrolytic oxidation layer is formed at that face as necessary, and thus a support web is formed. Next, a platemaking layer-forming liquid, such as a photosensitive layer formation solution, or a heat-sensitive layer formation solution, is coated onto a surface at the side of the support that has been dressed and is dried, and a photosensitive or heat-sensitive platemaking layer surface is formed.
Generally, a bar coater is employed for coating a coating liquid, such as a photosensitive layer formation solution, or a heat-sensitive layer formation solution, at a belt body, such as the aforementioned support web.
Conventionally, this bar coater is generally equipped with a bar and a coating section. While the bar is in contact with a lower surface of a continually running web, the bar rotates in a direction the same as the running direction of the web, or a direction opposite thereto. While the web is running, the coating section discharges the coating liquid at an upstream side from the bar, relative to the running direction of the web, and forms a coating liquid pool, thus coating the coating liquid onto the lower face of the web. The upstream side relative to the running direction of a web is hereafter referred to simply as “the upstream side”.
The bar coater may be a bar coater disclosed in Utility Model Registration No. 2,054,836 includes a dam plate which is provided in proximity with a bar at the upstream side of the bar, and is formed such that thickness at an upper end portion thereof becomes thin toward a downstream side in the running direction of the web. The upper end portion of the dam plate curves toward the bar, and includes a flat face with a length of 0.1 to 1 mm at a peak portion thereof. Another bar coater may be one disclosed in Japanese Patent Application Publication (JP-B) No. 58-004589, which includes a first dam plate which is formed such that thickness at an upper end portion thereof becomes thinner toward a downstream side. This bar coater is also provided with a second dam plate at the downstream side of the bar. The downstream side in the running direction of a web is hereafter referred to simply as “the downstream side”.
When the running speed of the support web becomes higher, an entrained air layer, which is a film of air that follows along and runs with the support web, that is, entrained air, is formed at the surface of the support web.
In either of the above-described bar coaters, when an entrained air layer is formed at the surface of the support web, the entrained air layer is carried into the coating liquid pool. As a result, the coating liquid is not applied to the surface of the support web uniformly, and coating of the coating liquid is not carried out stably, causing film discontinuities.
When the flow rate of the coating liquid which flows out from the gap between the bar and the dam plate is low, the flow of the coating liquid which overflows from the dam plate to the upstream side is intermittent, and is not uniform along the direction in which the dam plate extends, i.e., the widthwise direction of the strip-shaped body which is passing above the dam plate.
Accordingly, at the upstream side edge portion at the dam plate, the phenomenon of drying and sticking arises in which the coating liquid, which has adhered to the dam plate, dries out and sticks thereto. The stuck matter which arises due to this drying and sticking is a cause of various problems in surface quality at the coated surface on which the coating liquid is coated, such as coating streaks which are stripe-like defects, the adhesion of stuck matter in which the stuck matter comes off of the dam plate and adheres to the coated surface, and the like.